Many of today's portable consumer devices, including palm-sized computers, games, flashlights, shavers, radios, CD players, phones, power tools, small appliances, tooth brushes, etc., are powered by rechargeable batteries. The batteries in these devices, which are typically of the nickel-cadmium, lead-acid, nickel-metal-hydride, or lithium-ion type, must be recharged periodically to enable the continued use of the devices.
There are several methods used in the prior art to recharge such batteries. For example, many manufacturers produce rechargeable batteries corresponding to conventional AAA, AA, A, B, C, and D sizes, which are typically recharged using a charger station that is adapted to charge a certain size battery or a plurality of different size batteries. In addition, many power tool manufacturers produce lines of portable tools energized by batteries that are not of the standard sizes listed above, but which often share a common form factor and voltage rating. These batteries are typically recharged by removing the battery from the tool and charging it in a specially-adapted charger specific to that manufacturer's line of tools and specifically designed to recharge batteries of that voltage. In order to recharge both conventional-size batteries and the more specialized portable power tool batteries, it is generally necessary to remove the batteries from the portable device and attach them to their respective chargers, and after they are recharged, the batteries must be reinstalled in the portable device. This task is unduly burdensome and time-consuming for the user.
In order to avoid the burden associated with the foregoing task, some portable consumer devices include a charge-conditioning circuit (either internally or externally) that can be used with a conventional power source, such as a wall outlet, to provide a conditioned direct current (DC) at a voltage suitable for recharging a battery contained in the device. For example, it is common for electric shavers to include a charge-conditioning circuit that enables a nickel-cadmium (or other type) battery retained in the shaver to be recharged by plugging the shaver into a line voltage outlet. Similarly, some flashlights have an integrated connector that allows them to be recharged by simply plugging them into a wall outlet. In addition, certain devices such as portable hand vacuum cleaners use a "base" charger unit for both storing the device between uses and recharging the battery. When the portable device is stored in the base unit, exposed terminals on the device are connected through contacts on the base unit to a power supply energized with line current, thereby providing a conditioned DC current to charge the battery within the portable device.
In all of the foregoing examples, as is true of the majority of devices that use rechargeable batteries, some sort of interface comprising an electrical connection (i.e., contact) is used to provide an appropriate DC voltage for recharging the batteries. However, the use of contacts to connect a battery to a recharging current is undesirable, as they are susceptible to breakage, corrosion, and may present a potential safety problem if used improperly or inadvertently shorted. The shape and configuration of these contacts are also generally unique to individual devices, or a manufacturer's product line, making it impractical to provide a "universal" charging interface that includes contacts.
Recognizing the problems with recharging batteries with current supplied through electrical contacts, several manufacturers now offer "contactless" battery-charging devices. These charging devices are generally of two types--inductive charging systems, and infrared charging systems. Inductive charging systems include an electromagnetic or radio frequency coil that generates an electromagnetic field, which is coupled to a receiver coil within the device that includes a battery requiring recharging. For use in recharging a battery in a handheld powered toothbrush, a relatively high-frequency current is supplied to the transmitter coil in a base for the handheld toothbrush, thereby generating a varying magnetic field at a corresponding frequency. This magnetic field is inductively coupled to a receiver coil in the toothbrush housing to generate a battery charging current. Another example of such a system is the IBC-131 contactless inductive charging system by TDK Corporation, which switches a nominal 141 volt, 20 mA (max) input current to a transmitter coil at 125 kHz to produce a 5 volt DC output at 130 mA in a receiver coil.
A different contactless system for charging batteries is an infrared charging system employing a light source as a transmitter and a photocell as a receiver. Energy is transferred from the source to the receiving photocell via light rather than through a magnetic field.
Both inductive and infrared charging systems have drawbacks. Notably, each system is characterized by relatively high-energy losses, resulting in low efficiencies and the generation of excessive heat, which may pose an undesirable safety hazard. Additionally, the transmitter and receiver of an inductive charging system generally must be placed in close proximity to one another. In the above-referenced TDK system, the maximum gap between the receiver and transmitter is 4 mm. Furthermore, in an infrared system, the light source and/or photocell are typically protected by a translucent material, such as a clear plastic. Such protection is typically required if an infrared charging system is used in a portable device, and may potentially affect the aesthetics, functionality, and/or durability of the device.
It would therefore be desirable to provide a contactless energy transfer apparatus suitable for use with portable consumer devices that allows a greater spacing between the transmitter and receiver elements, and provides improved efficiency over the prior art. Furthermore, it is preferable that such an apparatus provide a contactless "universal" interface for use with a variety of different types and/or different sizes of devices made by various manufacturers.